In recent years, accompanied by remarkable progress of magnetic recording technology, recording density of the magnetic recording medium is becoming higher due to increase in the drive capacity. However, for the magnetic recording medium with a longitudinal magnetic recording system which is widely used currently, an attempt to realize the high recording density makes the recording bit to be miniaturized, which requires such a high coercive force to the extent that makes the recording with the recording bit impossible. Therefore, a perpendicular magnetic recording system is being investigated as a means for solving these problems and increasing the recording density.
In the perpendicular magnetic recording system, the axis of easy magnetization is formed to be oriented perpendicularly to the medium surface in the magnetic film of the perpendicular magnetic recording medium and this system is suitable for high recording density. In the perpendicular magnetic recording system, a multi-layer recording medium having a magnetic recording film layer with an elevated recording sensitivity, a soft magnetic film layer and an intermediate layer has been developed. A CoCrPt—SiO2-based alloy is commonly used for this magnetic recording film layer, while a Co—Zr—Nb-based alloy and the like are used for the soft magnetic film layer. The intermediate layer described herein refers generally to a layer provided for the purpose of reducing the size of the crystal grain of the magnetic recording film layer and imparting anisotropy to the crystal orientation.
As the intermediate layer, a variety of Ni-based alloys, Ta-based alloys, Pd-based alloys, Ru-based alloys, and so on have been proposed and recently a Ni—W-based alloy has also been used. One of the roles of these intermediate layers is to control the structure of the magnetic recording film layer. For this purpose, it is said that reducing the size of the crystal grain of the intermediate layer is important. For example, an example of a Ru intermediate layer has been proposed as disclosed in “Structure Control of Perpendicular Magnetic Recording Film” (Fuji Jiho, Vol. 77, No. 2, 2004, p. 121).
In addition, it is considered that, in the Ni—W-based alloy, the recording density is good if the lattice constant of the thin film is in a range of about 3.53 to 3.61 (×10−10 m), although the detailed reason is not known.
Although good recording properties can be obtained if a perpendicular magnetic recording medium is produced by using the Ni—W-based thin film as the intermediate layer, it is required to reduce the size of the crystal grain of the Ni—W-based intermediate layer in order to realize much higher recording density. Nevertheless, there is no common knowledge at all regarding the element and the like to be added which may contribute to reducing the size of the crystal grain of the Ni—W-based thin film.